<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        h1,div{
            width:200px;
            height: 200px;
            background-color: rgba(255, 0,0, .5);
            padding: 20px;
        }
        h2{
            background-color: red;
        }
    </style>
</head>
<body>
    <h1>
        一级标题
    </h1>
    <div>
        <h2>div->h2</h2>
    </div>
</body>
</html>